The present invention relats to oil well pumping apparatus and, in particular, to brakes used to prevent rotation of the crank and counter-balance weights.
An oil pumping environment as wherein the present invention is particularly applicable is shown in FIG. 1. In such apparatus, a derrick 10 is erected adjacent an oil well head 12. A wire cable 14 extends from a hoist drum (not shown) over a crown block 16 to a travelling block 18, which in turn is connected to well tubing 20. A derrick man operating platform 22 is suspended from the derrick 10 by a guy line 24 to be disposed about the wire cable 14 rising upward from the oil well head 12. Personnel stand on the platform 22 to perform necessary functions as the well tubing 20 is raised or lowered by the wire cable 14 by means of the hoist drum (not shown).
When the oil well has been drilled, a pumping unit, generally indicated as 26, is positioned to move a pump rod extending through oil well head 12 up and down to, thereby, pump the oil from the well. Such pumping units 26 are generally configured generally as shown, comprising a pumping unit base 28 upon which is mounted a unit drive motor 30 connected to a gear box 32. The gear box 32 has a first shaft 34 projecting therefrom which is rotated by the unit drive motor 30. A crank 36 is mounted on the first shaft 34 for rotation thereby. A set of counterbalance weights 38 are attached to the crank 36 adjacent the end thereof furthest from first shaft 34. A walking beam 40 is mounted atop a set of Sampson posts adjacent the gear box 32. The end of the walking beam 40 closest to the gear box 32 is connected to the crank 36 by a Pitman arm 44. Thus, as first shaft 34 rotates, crank 36 is rotated in combination therewith. As crank 36 rotates, the walking beam 40 is reciprocally pivoted about the center on the Sampson posts. By positioning the opposite end of the walking beam 40 above the well head 12, that end of the walking beam 40 can be connected to a pump rod, which will then be reciprocally driven into and out of the oil well head 12 as the crank 36 rotates to, thereby, pump the oil.
Both at the time of installation and during later servicing of the pumping oil well, one or more operating personnel are required to stand on the platform 22 for such jobs as pulling tubing, pump rods, the pump, etc. for observance, or replacment if necessary.
As can be seen from FIG. 1, as the crank 36 rotates from the upper position labeled "A" to the ghosted lower position labeled "B", the end of the walking beam 40 closest to the oil well head 12 moves between an extremely lowered position labeled "A" and an extreme raised position shown ghosted and labeled "B". Because of equipment size limitations, the platform 22 must be positioned as shown, such that at some point in the travel of the end of walking beam 40 between the lowered position A' and the raised position B' the end of walking beam 40 is at or above the level of the platform 22. Thus, crank 36 must be maintained in a generally raised position adjacent postion A while the platform 22 is positioned above the oil well head 12. For this purpose, a second shaft 46 operably connected with gear box 32 extends therefrom. A friction brake assembly, generally indicated as 48, is connected to second shaft 46. By engaging friction brake assembly 48, the rotation of crank 36 can be frictionally impeded or stopped.
Friction brake assembly 48 is shown in greater detail in FIG. 2. Second shaft 46 has a cylindrical brake drum 50 concentrically attached thereto as with bolts 52. Brake shoes 54 are disposed within brake drum 50. Brake shoes 54 can be moved radially outward into frictional engagement with brake drum 50 to, thereby, tend to prevent the rotation of brake drum 50 and, thereby, second shaft 46 and, in association therewith, first shaft 34. As can be seen, such a system is not a positive locking device and, therefore, presents a safety hazard to the operating personnel. Slippage or inadvertent release of the brake shoes 54 from the frictional engagement with brake drum 50 will allow crank 36 to move from position A to position B and, correspondingly, walking beam 40 to move from position A' towards position B' and, thereby, strike platform 22.
Yet another form of prior art braking mechanism employing an unsuccessful positive lock is shown with reference to FIGS. 9-11. In this type of brake, shaft 46 has a large metallic drum 110 attached thereto. A braking band 112 is disposed about the periphery of the drum 110 being held on one side by a bracket 114 mounted to a pivot pin 116. The two ends of braking band 112 meet on the opposite side in spaced relationship with one side connected to a flexible sleeve 118 and the opposite side connected to a flexible cable 120 slidably disposed within the flexible sleeve 118. By pulling the flexible cable 120 into the flexible sleeve 118, the braking band 112 can be compressed about the metallic drum 110 to cause a sliding braking action similar to the brake shoes 54 acting on the inside of the cylindrical brake drum 50 in the embodiment of FIG. 2 described above.
In addition, however, the braking band 112 covers only a portion of the width of the periphery of the metallic drum 110. Adjacent the rear surface thereof, a series of shallow recesses 122 are formed therein. A heavy iron locking bar 124 is pivotally mounted on one end to a pivot pin 126 mounted parallel to shaft 46. Locking bar 124 contains a projection 128 on the end opposite pivot pin 126. Projection 128 is adapted to fit into the shallow recesses 122 when locking bar 124 is rotated from the position shown in FIG. 9 to the ghosted position shown in FIG. 9.
While it was probably intended that braking units for well pumps configured as shown in FIGS. 9-11 would provide an additional margin of safety not contained in units configured with only a sliding brake, such is not the case. In actuality, the providing of the "locking" bar 124 which is not sufficient for its intended purpose may, in fact, create a bigger hazard than having it omitted. This is clear from the typical warning tag which is attached to the locking bar 124 as indicated by arrow 130 in FIG. 9, or attached adjacent thereto. The text of an actual tag as copied by applicant from such apparatus read as follows: "BE CAREFUL--the pumping unit brake is not intended as a safety stop, but is intended for operational stops only--apply brakes slowly. Sudden stops may damage equipment. When operations or maintenance are to be conducted in or around the pumping unit, the position of the crank arms and counterweights should be fixed securely in a stationary position by chaining or other acceptable means-".
Clearly, therefore the locking bar 24 and its relationship with shallow recesses 122 does not provide a satisfactory safety brake for such apparatus. A satisfactory safety brake meeting OSHA requirements for a safety brake does not exist in the art at present. As can be understood, locking bar 124 can be manipulated only by personnel moving in close proximity to the large rotating members of the pumping apparatus. There is no bias on locking bar 124 tending to hold it either into engagment with the shallow recesses 122 or in a safely removed position therefrom when the machine is normally operating. It is typical that because of the vibrations attendant to the operation of such machinery locking bar 124 falls onto metallic drum 110 as the apparatus is rotating causing the edges of the shallow recesses 122 and the projection 128 of locking bar 124 to become rounded as shown as shown by the arrows 132 in FIG. 11. As thus configured, any rotary pressure against the projection 128 by the turning of drum 110 in the direction of arrow 134 creates a vertical force, as symbolized by the arrow 136, tending to pull the projection 128 out of the shallow recess 122 into which it has been inserted.
Wherefore, it is the primary objective of the present invention to provide a positive lock to prevent the rotation of crank 36 during periods of installation and servicing.
It is a further objective of the present invention to provide a positive lock for such oil pumping apparatus which is easily adaptable for attachment to existing apparatus.
It is yet another object of the present invention to provide a positive lock for oil well pumping apparatus which is readily and safely releasable under extreme holding forces imparted by the large counterbalance weights employed in such apparatus.